Actuators of rigid electrically actuatable material provide articulation for robotic limbs. Piezoelectric actuators, for example, may be used in various embodiments of robotic joints (8) to rotate a cylindrical or spherical connection or to translate a rod. Opposing pairs of actuators (30) engage in smooth walking motion and maintain a vise-like grip on the robot limb (12) at all times. The traction surfaces of the actuators contact the robot limb with zero clearance. Unlike the use of conventional bearings, zero clearance and full area contact provide relatively large mechanical stiffness that allows very precise positioning of robot limbs without mechanical oscillations of the extremities. With adequate limb rigidity, slop is essentially eliminated from the joints. The smooth walking motion of the actuators achieves high mechanical efficiency by eliminating sliding friction. The joints operate in air or space vacuum without lubrication and with negligible heating. Relatively large forces and torques are developed at relatively slow speeds. Size of the robotic joints can range from relatively large to microscopic. IMAGE
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